3) I look for things to argue about, such as checking his texts, his email, etc then asking him who the people he was talking to are.

2 and 3 I will work on. #1 is the one I am having a hard time with. His sister hates me and is constantly calling me names, degrading me, talking trash about me to other people, lying and making up stories about me and telling people. She has even tried to set him up with her friend in an attempt to get us divorced (her words, not mine). She has now started verbally abusing our kids and talking about them as well. It is very hard for me not to complain when she does these things. I am torn between trying to make him happy by not complaining about what she says and does, and protecting my kids. They are 15 and 17 and when she says hurtful things to them or about them (on FB or to other people) I turn into a momma lion and try to protect them. How do I make it through this?

Through this journey you will learn to take the high road and learn to forgive even her. And that testimony is what will be big in the eyes of everyone around you, including her. Leave those things to Christ, there is nothing you can do to control that.